Tissue repair materials for the repair or replacement of connective tissue have existed for some time. These materials can be synthetic or biological materials or combinations thereof. The most common of these are ligament augmentation devices and ligament replacement devices for the repair or replacement of damaged cruciate ligaments. These devices are typically implanted by drilling a through-hole into the proximal end of the tibia and another through-hole into the distal end of the femur. The tissue repair device is pulled through these two holes, the two ends of the device extending some length beyond the extreme ends of the through-holes and secured to adjacent bone, typically with bone screws, staples, sutures or combinations thereof.
In the case of the repair or replacement of the anterior cruciate ligament, the through-hole in the proximal end of the tibia is typically drilled from below, the drill entering the anteromedial side of the tibia and emerging at the anatomic attachment site on the tibial plateau. The corresponding through-hole in the distal end of the femur is typically drilled in one of two locations, chosen according to the intended placement of the ligament repair device. "Anatomic placement" of the device requires a through-hole drilled from the lateral femoral epicondylar area and emerging at the origin of the anterior cruciate ligament on the posteromedial aspect of the lateral femoral condyle. The alternative placement of the tissue repair device is called "over-the-top" placement which may or may not necessitate a femoral through-hole. In the case requiring a femoral through-hole, the through-hole begins at a point four or five centimeters proximal to the lateral femoral epicondyle on the lateral shaft of the femur. The through-hole is directed posterior, medial and inferior to exit at a point just proximal to the capsular attachment and lateral to the midline of the axis of the femur.
In recent years it has become apparent that a high degree of precision is required to assure proper placement of the drilled through-holes if tissue repair materials are to function properly and reliably. As both the entry and exit site of each through-hole are subject to error due to the relatively poor access and difficulty in recognizing correct orientation during this type of surgery, several different types of drill guides have been designed to reduce the likelihood of error.
These drill guides may be divided into two categories, the first being guides that drill the tibial and femoral through-holes independently with the result that the relative locations of the two holes with respect to each other are not assured. Most commercially available drill guides at present are designed to function in this manner. By failing to provide for the proper relationship between the two holes, the use of these drill guides often results in an abrupt angle between the segment of the tissue repair device located between the drilled through-holes, called the intra-articular segment, and the portions of the device located within the through-holes. This abrupt angulation can result in premature wear and failure of the tissue repair material as the material works in tension over the edges of the drilled through-holes.
In addition, these types of drill guides suffer from various combinations of the following problems: (1) inadequate rigidity, (2) moveable joints allowing excessive flexibility, (3) locating probes subject to inaccurate placement, (4) inability to provide for both anatomical and over-the-top ligament placement, (5) insecure attachment of the drill guide to the bone surface resulting from lack of gripping features on the appropriate drill guide surface, inadequate securing force or securing force applied other than axially to the drill guide, and (6) axial orientation of locating probe tip and drill guide without a planar third point reference to the desired bone surfaces.
The second type of drill guide makes an attempt to align the femoral and tibial through-holes. At this time only a few such devices are available. With these drill guide systems, a single drilling is performed to create both the tibial and femoral through-holes on the same axis. One of these devices consists of two extra-articular and one intra-articular guide posts attached to a common cross-bar. The drill pilot, attached to the end of an extraarticular guide post opposite the end slideably attached to the cross bar, is axially secured without teeth using a screw to provide secure location. Because it locates primarily from its intra-articular guide post in a pivotal fashion and because both extra-articular guide posts are slideably mounted, the drilled through-holes may be correctly centered by the intra-articular guide post but angularly mis-located by improper location of the extra-articular guide posts on the cross-bar.
Another such device that relies on the concept of tibial and femoral through-holes drilled on the same axis uses a guide that clamps between the surfaces of the tibial plateau and the anterior face of the femur. In use with this device the knee is bent to an angle of about ninety degrees. This drill guide is subject to inaccurate placement and does not provide for a secure attachment to the tibia.
There are several fundamental problems with present drill guides designed to drill tibial and femoral through-holes on a common axis. They only provide ideal alignment of the tissue repair device when the knee is highly flexed, at which position it is typically under lower load. When the leg is straightened and highly loaded the tissue repair device is most severely angulated. These devices can also cause misalignment between the two holes because the femur and tibia, connected by a damaged or broken anterior cruciate ligament, are subject to lateral displacement relative to each other during drilling. Additionally, these drill guides are only capable of anatomical placement of a tissue repair device and cannot provide for over-the-top placement.